Plastics identification

ABSTRACT

To enable a spectrometer (10) to be used for taking analysis readings from plastics articles (24) of varying shapes and degree of preparation, the spectrometer (10) is enclosed within a housing which has an interface device (14) attached to the sensing window (58). The interface device (14) is sensitive to the positioning of a sample (24) in position to carry out sample preparation tasks as the sample is brought into the analysis position opposite the sensing window (58). The interface device (14) comprises a front wall (16) with a sample aperture (18) against which the sample (24) can be placed so that a surface of the sample (24) is exposed through the aperture (18), means (48) for cleaning a sample surface (24) placed against the front wall (16), means (52) for extracting debris resulting from the sample cleaning, and means (30, 32) for guiding the front wall (16) towards the sensing window (58) to enable the spectrometer (10) to take a reading from the sample surface (24).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus for identifying differentplastics materials. The apparatus is particularly (but not exclusively)suitable for use in the plastics industry, for separating plasticscomponents into chemically similar groups as a first stage in, forinstance, the recycling of the plastics materials.

2. Description of the Related Arts

One field of application is the recycling of motor car components. Whena motor car is scrapped, its saleable components such as battery, tiresor radio are removed, usually for use in other vehicles. The metal partsof the scrap car are generally re-cycled, and what remains is shreddedand used as land-fill.

The remainder that is used for land-fill consists primarily of a mixtureof plastics materials. For environmental and/or economic reasons, it isdesirable to be able to recycle such waste plastics materials. Howeverit is not possible effectively to recycle mixtures of waste plasticswithout first separating the plastics into chemically similar groups orfamilies. Failure to achieve this separation would mean that unknownportions of different plastics were incorporated in the melt during thereclaim process. The presence of other plastics components in a blendmay necessitate changes in processing conditions or lead to unacceptablechanges in the physical properties of the finished recycled material.

Whilst a number of laboratory techniques are known for identifyingdifferent plastics materials, none of these are suitable for use in acontinuously operating plastics recycling line, and none of them cancope easily with scrap motor car parts which are of irregular size andshape and are usually dirty.

European patent publication number 0 497 397 discloses apparatus foridentifying plastics materials, the apparatus comprising a light sourcefor producing short wave light impulses, spectral apparatus forproducing an emission spectrum, a detector for converting the radiationintensities into electrical signals, and a computer for processing theelectrical signals to produce sorting signals. The apparatus is usedwith particles of plastics materials which are carried by a conveyorbelt from a delivery station. When a particle of plastics materialpasses a pre-set point by the apparatus it breaks a light beam,triggering the light source to take a reading. The reflection spectrumfrom a plastics material is used to identify that material and allowlike materials to be sorted together. The surface of a particle ofplastics material may be partially cleaned by means of a laser beam toremove surface dirt.

Our co-pending International Patent Application number PCT GB93/02244describes a method and an instrument for identifying plastics materialsusing a spectroscopy technique.

While spectroscopy can lead to accurate results in terms of plasticsidentification, the instrumentation required is delicate and has to becarefully set up and maintained.

The present invention therefore seeks to provide an interface betweenspectroscopy apparatus and a piece of plastics to be identified, whichwill allow plastics components of a wide variety of shapes andconditions to be brought into a uniform position where they can betested by the apparatus.

SUMMARY OF THE INVENTION

According to the present invention, there is provided apparatus foridentifying plastics, the apparatus comprising a spectrometer,characterised in that the apparatus further comprises a protectivecasing surrounding the spectrometer with a sensing window formed in oneface of the casing, and an interface device associated with the sensingwindow, the interface device comprising a front wall with a sampleaperture against which the sample can be placed so that a surface of thesample is exposed through the aperture, means for cleaning a samplesurface placed against the front wall, means for extracting debrisresulting from the sample cleaning, and means for guiding the front walltowards the sensing window to enable the spectrometer to take a readingfrom the sample surface.

It is a feature of the invention that the sample is positioned once onthe front wall, and thereafter only needs to be held in contact with thefront wall and pushed forward with the front wall until the reading hasbeen taken.

The guiding means preferably comprises a set of tracks along which thefront wall can move linearly towards the sensing window, with the frontwall being urged to the end of the tracks remote from the window.

The chamber is preferably surrounded and possibly enclosed by side wallsin the form of collapsible bellows. The front wall may be displaceabletowards and away from the sensing window of the spectrometer casing, andthe displacement may be accomplished by mounting the front wall onspring-loaded guide rods which allow the front wall to be moved towardsthe sensing window, up to a defined end position at which a spectrometerreading will be taken.

The sample surface cleaning means, the debris extraction means and thepurging medium feed means, when present, may all be sequentiallyoperated by switches which are tripped in turn as the front wall isdisplaced towards the sensing window of the spectrometer casing. Themechanisms for sample surface cleaning, for debris extraction and forintroduction of purging medium may all be constructed in such a way thatthey are brought into position between the front wall and the sensingwindow, when they are operated, and are automatically moved out of theregion between the front wall and the sensing window when their functionhas been completed.

The sample surface cleaning means may be a grinding wheel, router orsimilar device which rotates in contact with the sample surface throughthe sample aperture of the front wall.

The debris extraction means can be a suction pipe which uses suction toextract debris, particularly debris produced by the action of the samplesurface cleaning. The debris extraction means may operate simultaneouslywith the sample surface cleaning means.

In a preferred embodiment the sample surface cleaning means is containedwithin a housing inside the interface device chamber. The housing may beprovided with means for sweeping away and collecting swarf which isproduced by the cleaning of the sample surface. The housing may beprovided with a tube or other conduit through which the swarf passes tobe collected by collection means. A partial vacuum may be applied viathe tube to help with the removal of swarf from within the housing bysuction. This embodiment permits more efficient collection and removalof swarf.

The purging medium feed means will preferably fill the chamber with aninert medium at a positive pressure, prior to the spectrometer readingbeing taken. The use of a positive pressure will prevent ingress ofparticles into the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic view of a plastics identification apparatusaccording to the invention, and also showing a plastics item to beidentified;

FIG. 2 is a cross-section through part of the apparatus of FIG. 1;

FIG. 3 is a cross-section through a part of a preferred grinder housingarrangement for use with the apparatus of FIG. 1; and

FIG. 4 is a view corresponding to FIG. 1 but showing a second embodimentof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a spectrometer 10 indicated in dotted lines which is housedwithin a protective housing 12. The protective housing protects thedelicate spectrometer instrument from dirt and other foreign matter andfrom physical shocks. The housing is therefore continuous around thespectrometer instrument, apart from a sensing aperture or window 58through which the spectrometer can look at a sample to be analysed.

On one face of the casing 12 there is a sample interface device 14. Thisdevice consists of a front wall 16 with a sample aperture 18, a backwall 20 mounted on the outer surface of the housing 12 and a flexiblebellows 22 which encloses a chamber between the front wall 16 and theback wall 20. The back wall has an opening 57 which is closed by ashutter 56, and which registers with the sensing window 58 of thehousing 12.

A sample to be identified, in this case a motor vehicle bumper 24, isplaced against the sample window 18, as will now be described withreference to FIG. 2.

In FIG. 2 the vehicle bumper 24 (which has a curved rather than a flatsurface) is placed against the front wall 16 so that it covers thesample aperture 18. It may be desirable to place a compressible rubberseal 26 around the aperture 18 so that part of the bumper 24 within theseal is sealed against the outside environment.

To take a reading, the operator holds the bumper 24 against the frontwall 16 and exerts pressure on the bumper which gradually pushes thebumper and the front wall towards the protective housing 12. The frontwall is mounted on guide rods 28, 30 which are biased away from thehousing 12 by compression springs 32, 34. The force of these springs canhowever be overcome by the pressure which the operator exerts on thebumper.

As the inner ends of the guide rods 28, 30 pass into the interior of thecasing 12, a foot 36 on the rod 30 moves past switch levers 38, 40, 42,44 on a switch mounting arm 46. After the first stage of inwardmovement, the switch lever 38 is tripped and this triggers operation ofa grinding wheel 48 which rotates to grind a clean surface area on thebumper. The purpose of this grinding step is to remove any surfacetreatments such as paint and/or surface grime which may have accumulatedon the surface.

As the movement of the front wall 16 towards the housing continues, thefoot 36 will next operate the switch lever 40 which will stop operationof the surface cleaning, will cause the grinding wheel to be moved awayfrom the sample aperture, and will start a debris extraction routinewhich extracts any debris contained within the chamber 50 through asuction pipe 52.

When the foot 36 reaches the third switch lever 42, debris extractionwill stop, the pipe 52 will be moved away from the sample aperture, andthe chamber 50 will be purged by introducing an inert gas through a gaspipe 54.

Finally when the foot 36 reaches the last switch lever 44, purging willstop, the pipe 54 will be withdrawn, a shutter 56 which closes a sensingwindow 58 will be opened, and the spectrometer itself will be activatedto take a reading of the clean bumper surface 24.

Once the reading has been taken, a signal is given to the operator,possibly by the illumination of a green light somewhere on the casing,that the bumper can be removed and the springs 32, 34 will then restorethe front wall 16 to its original position and the apparatus will beready for another sample to be put in place and another reading to betaken.

FIG. 3 shows a preferred assembly for cutting a clean surface on asample. A rotatable cutting blade 480 is mounted on a spindle 60, andthe spindle is provided with two sweeping members 64. The assembly iscontained within a housing 62 which is connected to a tube 66 forconveying swarf to a swarf bin. In operation the blade 480 cuts or millsthe sample surface, and the sweeping members 64 act to sweep swarf fromthe sample surface down the tube 66 to a bin (not shown). Suction may beapplied to the tube 66 to aid in swarf removal, and the assembly may beused in addition to, or instead of, the debris extraction routinedescribed above.

FIG. 4 shows an alternative embodiment where the space between the frontwall 116 and the spectrometer casing 112 is not enclosed.

The spectrometer casing has a turret 111 and the sensing window 158 isat the tip of this turret. In this embodiment, no steps are taken topurge the atmosphere surrounding the turret, but a pipe 152 is used toextract dust and swarf from the prepared sample surface. This pipe 152can be housed, in part, in the space surrounding the turret 111.

The front wall 116 is mounted on posts 128, 130 surrounded by coilsprings 132, 134. There are three of these posts. The fourth corner ofthe front wall is not supported by a post but is designed to allowaccess to a milling cutter 148 which is mounted on a swing arm 149. Thefront wall 116 has an arcuate track 151 to allow entry of the cutter 148to a position where it cuts the sample surface directly in the positionwhere the sample will register with the sensing window 158. The cutterwill be set slightly proud of the front wall 116 and will cut a trackthrough the sample surface as it swings in. The rotation of the cutterand the movement of the swing arm can both be started by a contactswitch which is triggered when a sample is placed against the front wall116.

The cutter could alternatively move along a linear path to the centre ofthe front wall 116.

The space between the front wall 116 and the spectrometer housing couldbe shielded on two or three sides to restrict dust entry and to improveappearance.

A shutter over the sensing window 158 will be opened automatically whenthe front wall 116 is pushed up against the turret 111, to enable thespectrometer to take a reading from the prepared sample surface.

Although a spectrometer can produce very accurate results in respect ofplastics identification, a spectrometer instrument is a delicateinstrument, the setting and handling of which requires considerableskill. Using an interface as described here between the spectrometer andthe sample to be identified allows the spectrometer to be isolated fromthe environment and yet to be used for taking quick readings of a numberof different samples.

We claim:
 1. An apparatus for identifying different plastic materialscomprising;a spectrometer (10), a protective casing (12, 112),surrounding the spectrometer (10) and defining a sensing window (58,158) formed in one face of the casing (12, 112); an interface device(14) associated with the sensing window (58, 158), of the interfacedevice (14) having a front wall (16, 116) defining a sample aperture(18, 118) against which a sample (24) can be placed so that a surface ofthe sample (24) is exposed through the aperture (18, 118); means (48,148, 480) for cleaning a sample surface (24) placed against the frontwall (16, 116); means (52, 152) for extracting debris resulting from thesample cleaning; and means (28, 30, 128, 130) for guiding the front wall(16, 116) towards the sensing window (58, 158) to enable thespectrometer (10) to take a reading from the sample surface (24).
 2. Theapparatus as described in claim 1, wherein the guiding means (28, 30,128, 130) comprises a set of tracks along which the front wall (16, 116)can move linearly towards the sensing window (58, 158), and the guidingmeans being provided with means (32, 34, 132, 134) for urging the frontwall (16, 116) to the end of the tracks remote from the window (58,158).
 3. The apparatus as described in claim 2, wherein the tracks areposts (128, 130) surrounded by coil springs (132, 134), with the springs(132, 134) normally urging the front wall (116) away from the sensingwindow (158), and being compressed when the front wall (116) is movedtowards the window (158).
 4. The apparatus as described in claim 3,wherein a chamber (50) is enclosed by the front (16), a back wall (20)and by side walls, the side walls include a collapsible bellows (22). 5.The apparatus as described in claim 4, further comprising means (52,152) for extracting debris resulting from the sample surface cleaning isprovided between the front wall (16, 116) and the sensing window (58,158).
 6. The apparatus of claim 5, wherein the debris extraction meansis a suction pipe (152) which uses suction to extract debris,particularly debris produced by the action of the sample surfacecleaning.
 7. The apparatus is claimed in claim 5, wherein the debrisextraction means (152) is adapted to operate simultaneously with thesample surface cleaning means (480).
 8. The apparatus as described inclaim 4, further comprising means (54) for feeding a purging medium intothe enclosed chamber (50).
 9. The apparatus as described in claim 8,further comprising a turret (111) extending from the spectrometer casing(112) having the sensing window (158) at the end of the turret. (111).10. The apparatus of claim 8 further comprising a switch (38) which istripped as the front wall (16, 116) is dispensed towards the sensingwindow (58, 158) of the spectrometer casing (12, 112) and operates thesample surface cleaning means (48, 148, 480).
 11. The apparatus isdescribed in claim 10 further comprising switches (38, 40, 42) which aretripped as the front wall (16) is dispensed towards the sensing window(58) of the spectrometer casing (12) and engage a sample surfacecleaning means (48, 480), the debris extraction means (52) and thepurging medium feed means (54).
 12. The apparatus as described in claim11, wherein the mechanisms for sample surface cleaning (48, 480), fordebris extraction (50) and for introduction of purging medium (52) areall moveable between the front wall (16) and the sensing window (58).13. The apparatus of claim 8, wherein the purging medium feed (54) meansis adapted to fill the chamber (50) with an inert medium at a positivepressure, prior to the spectrometer reading being taken.
 14. Theapparatus of claim 1, wherein the sample surface cleaning meanscomprises a rotary cutter (480).
 15. The apparatus of claim 1, whereinthe sample surface cleaning means is a grinding wheel (48) which rotatesin contact with the sample surface through the sample aperture (18) ofthe front wall (16).
 16. The apparatus of claim 1, wherein the samplesurface cleaning means (480) is mounted in a housing (62) which isconnected by means of a conduit (66) to a debris collection bin andwherein the surface cleaning means (480) is provided with sweeping means(64) for sweeping debris into the conduit (66).